Travelling wave chain antenna

ABSTRACT

A travelling wave chain antenna including a ground plane, having a radiation beam, the direction of which can be varied by altering the frequency, wherein the antenna consists of foursided links made of conducting material and of connection parts between the links, these being located one after another, either in a straight row, in such a manner that the connection parts are at right angles to the longer sides of the links, or in an oblique row, in such a manner that the connection parts are at an angle to the longer sides of the links, the center points of the longer sides of the links being electrically connected to the center point of the longer side of the following link by means of the connection parts which are parallel to the shorter sides of the links, and the antenna being fed from either end by means of a cable, in such a manner that one conductor is connected to one end of the chain structure of the antenna and the other conductor is connected to the ground plane, the end of the antenna opposite the feed point being either open or loaded with a load impedance connected between the end of the antenna and the ground plane.

United States Patent 1191 Tiuri et al.

[ TRAVELLING WAVE CHAIN ANTENNA 22 Filed: Sept.28,l972

21 Appl. No; 294,448

52 us. c1 343/731, 343/846, 343/853 51 Int. Cl. H0lq 11/02 I [58] Fieldof Search 343/7925, 846, 897, 908,

[56] References Cited UNITED STATES PATENTS 3,290,688 12/1966 Kraus343/897 3,123,827 3/1964 Arnold et al 343/7925 Primary Examiner-EliLieberman Attorney, Agent, or Firm-Eric H. Waters [451 Apr. 23, 1974 [57] ABSTRACT A travelling wave chain antenna including a ground plane,having a radiation beam, the direction of which can be varied byaltering the frequency, wherein the antenna consists of four-sided linksmade of conducting material and of connection parts between the links,these being located one after another, either in a straight row, in sucha manner that the connection parts are at right angles to the longersides of the links, or in an oblique row, in such a manner that theconnection parts are at an angle to the longer sides of the links, thecenter points of the longer sides of the links being electricallyconnected to the center point of the longer side of the following linkby means of the connection parts which are parallel to the shorter sidesof the links, and the antenna being fed from either end by means of acable, in such a manner that one conductor is connected to one, end ofthe chain structure of the antenna and the other conductor is connectedto the ground plane, the end of the antenna opposite the feed pointbeing either open or loaded with a load impedance connected between theend of the antenna and the ground plane.

17 Claims, 9 Drawing Figures TRAVELLING WAVE CHAIN ANTENNA Thisinvention relates to high gain travelling wave antennas having a groundplane and in which the direction of the radiation beam generally dependson the frequency.

When a high gain antenna is required, especially in the HF, VHF, UI-IFand SHF ranges, dipole arrays are generally used. When the number ofdipoles is large, however, the feed system for the antenna array becomesextremely complicated and expensive. Also the band width of the assemblyis in general seriously limited by the feed system. The travelling waveantenna has the advantage of a simple feed system. One disadvantage ofprevious antennas of this type, such as the long-wire antenna, V-antennaand rhombic antenna, is that the direction of the radiation beam isdetermined by the length of the antenna, and therefore the beam from theantenna cannot be freely directed in the desired direction. Also, inorder to achieve a narrow beam, the length of a long-wire antenna, forexample, must be several wavelengths. The resulting radiation pattern isfinger shaped, or in other words, has several side lobes in addition tothe main beam.

Some of the earlier resonant-type antennas used especially in the shortwave range can be fed at a single point. These include the Franklinantenna, the Sterba array and the Bruce array (Jasik: AntennaEngineering Handbook, Chapters 4 and 21). As these antennas are of theresonant type, they operate efficiently only at one frequency, andgenerally only as broadside arrays. Because of the difficulties incontrolling the radiation properties of these antennas, their length islimited, in practice, to a few wave lengths, and the beam width cannotbe greatly reduced.

The wire mesh antenna described by JD. Kraus (U.S. Pat. No. 3,290,688)consists of a wide network made up of rectangular wire meshes and fed ata single point. A disadvantage of this antenna is that it is not powermatched. This causes a decrease in gain and an increase in the back beamdue to reflections. The distribution of the current at the feed in endof the antenna is only good when operating at the middle frequency, and,in addition, the antenna cannot be used with circular polarization.

An object of the antenna provided in accordance with the invention is toeliminate the aforementioned disadvantages. it is characteristic to theinvention that the antenna is a travelling wave, chain shaped antennalocated above a ground plate, the radiation properties of which caneasily be controlled. The structure of the antenna is simple and itrequires only one feed point.

By varying the frequency, the radiation beam of the.

antenna can be rotated over a large area. A high gain can be achievedwith this antenna if required, and also a narrow beam, without theoccurrence of strong, interfering side lobes. The antenna can easily beused as an element in large antenna arrays, and can be used both for thetransmission and reception of linear or circular polarization.

The invention is described in detail in the following with reference tothe attached drawing in which:

FIG. I shows a plan view of the basic arrangement of the antenna;

FIG. 2 shows a side view of the basic'arrangement of the antenna;

FIG. 3 shows an antenna having parallel-sided links;

FIG. 4 shows an antenna in which the distance from the ground planevaries continuously;

FIG. 5 shows an antenna having a radiation structure of increasingdimensions;

FIG. 6 shows an antenna in which alternate links are of equal size;

FIG. 7 shows a parallel connection of two chain antennas;

FIG. 8 shows a parallel connection of two chain antennas; and

FIG. 9 shows a parallel connection of two chain antennas, to obtaincircularly polarized radiation.

As shown in FIGS. 1, 2 and 3, the basic arrangement of the antennaconsists of a chain shaped structure 1 made of electrically conductivematerial, located above a ground plane 2 made of electrically conductivematerial. The chain is made up of links 3 and connection parts 6electrically connected to them. The four-sided links 3, which arerectangular as in FIGJI or parallelograms as in FIG. 3 are arranged in arow in such a manner that the longer sides 4 of the links are parallelto each other and the midpoints of all the longer sides lie on the sameline. The midpoints of the longer sides of adjacent links are connectedto each other by means of connection parts 6. Ground 2 is, for example,a solid metal sheet, a perforated metal sheet, a wire net having a meshsize of 0.1 wavelengths or a grid made up of wires located side by sideand parallel to parts 5 and 6. Typical dimensions for the antenna, inwavelengths corresponding to the middle frequency of the operatingrange, are as follows: the shorter sides 5 of the links and theconnection parts 6 between the links, 0.4 wavelengths, the longer sides4 of the links, one wavelength, the distance from the ground plane, 0.1wavelengths and the total length of the antenna, for'example, l0wavelengths. The antenna is fed at one end 7 of the chain by means of acoaxial cable, for example, in such a manner that the center conductor16 (16') is connected to the chain structure 1 and'the outer conductor15 (15') to the ground plane 2. Feeding can also be effected by means ofa twin conductor structure.

The antenna can also be fed at both ends. Several receivers ortransmitters operating at different frequencies can be connectedsimultaneously to the antenna.

Measurements have shown that an antenna constructed in accordance withthe dimensions given above radiates in such a manner that the maximumbeam is directed ata backward elevation angle of 0 at the middlefrequency. Alteration of the frequency by i 10 percent causes therotation of the beam over the range 0 45 without the gain of the antennachanging considerably.

It is essential to the operation of the antenna that there exist a powerwave moving'away from the feed point of the antenna. For this reason, inan ideally constructed antenna, the characteristic impedance of thetransmission line made up of parts 6 and the ground plane must be halfthe characteristic impedance of the transmission line made up of parts 4and 6 and the ground plane. This condition can be fulfilled in a mannerof ways such as, for example, by making parts 6 of considerably thickersections than parts 4 and 5, by making parts 6 of broad flat sections orof two or more adjacent wires, by decreasing the distance between theground plane and parts 6 or in some other way in which the inductance ofparts 6 is decreased or the capacitance between parts 6 and the groundplane is increased. Tests with various antennas have shown that thefulfillment of the above-mentioned impedance condition within anaccuracy of approximately 10 percent is sufficient for the more usualantenna applications. In an antenna of middle frequency 3 GHz, havingparts 4 and 5 made of 0.5 mm diameter round wire and parts 6 made of 0.5X 10 mm flat section, a power wave, ideal within the limits ofmeasurement accuracy, moving away from the feed point has been measured.

When the above-mentioned impedance condition is fulfilled the wholeantenna can be represented as a transmission line with losses, having aconstant impedance and with the size of the losses depending on theradiation power per unit length of the antenna. If the impedancecondition is not fulfilled, power reflections occur in the transmissionline and the power wave reflected backwards causes a back beam in theradiation pattern and a decrease in the main beam. The back beam, causedby the power wave reflected from the end opposite to the feed end of theantenna can be eliminated by loading the further end of the antenna.This can be done, for example, using a termination 17 equal to thecharacteristic impedance of the antenna, by placing absorbing materialbetween the far end of the antenna and the ground plane or by making theantenna sufficiently long.

The radiation properties of the antenna can be controlled by varying thedistance to the ground plane. An increased distance gives greaterradiation power per unit length of the antenna, and a smaller distanceto the ground plane means lower radiation power per unit length of theantenna. A chain antenna which is long in comparison to the wavelengthis located near the ground plane such as, for example, at a distance of0.05 wavelengths from it, and thus a high gain and a narrow beam isachieved. A shorter antenna having a smaller gain and a wider beam islocated further away from the ground plane, for example at a distance of0.15 wavelengths. The radiation power per unit length can also beincreased by bending parts 5 and 6 into upward curved shapes in such afashion that the middle sections of the parts are further away from theground plane than their ends, or by otherwise arranging that parts 5 and6 are further away from the ground plane than parts 4, over their wholeor partial length.

The distribution of the current in the antenna can be improved, at thesame time increasing the efficiency of the antenna, by increasing thedistance from the ground plane either in steps or continuously whenmoving away from the feed point of the antenna. A side view of such achain antenna is shown in FIG. 4. The shortest distance from the groundplane can be approximately 0.05 wavelengths and the maximum distanceapproximately 0.25, wavelengths. The total length of this type ofantenna can be approximately 20 wavelengths. i

The current distribution and the radiation properties of the antenna canbe altered by making the ground plane or the radiating antenna structureitself, or both of them curved. If, for example, the ground plane andthe antenna are both curved in the same direction in the plane parallelto the longitudinal axisof the antenna, and the antenna is on'theconcave side of the ground, the beam from the antenna can be angled atthe same direction over the whole range of operating frequency and, ifthe antenna is on the convex side of the ground, a circular radiatingantenna of large angular range is achieved.

The geometrical shape of the antenna has proved to be such that thelonger parts 4 of the links cancel each other out almost completely, andthe shorter parts 5 and connection parts 6 function as efficientradiation elements. From a functional point of view, parts 4 of theantenna are transmission lines which cause additional phase shift whenmoving to the next radiation element.

The direction of the main beam can be set at the desired angle at themiddle frequency by dimensioning the parts so that parts 4 have a lengthof one wavelength and parts 5 and 6 are 0.25 0.75 wavelengths. Theelevation angle 0 of the radiation beam, measured as shown in FIG. 2, issmall when the length of radiation elements 5 and 6 is small, and largewhen the elements are long. When parts 5 and 6 have a length of 0.3wavelengths, for example, the angle of elevation 0 is approximately 48,and when they are 0.4 wavelengths long the angle is The mathematicalformula which gives the approximate direction of the beam is where n isan integer, k is the wavelength, I is the length of parts Sand 6'and Iis the lengths of parts 4.

A certain phase shift takes place between two adjacent radiatingelements 5 and 6 due to the physical dimensions of the antenna. Theelectrical length between the beginning point of part 5 and thebeginning part of the following part 6 can be increased or decreasedartifically, thus altering the direction of the main beam at a certainfrequency. Conventional electrotechnical methods of altering the phaseshift can be used, such as using a variable series inductance or a shuntcapacitance. The additional phase shift can also be made adjustable sothat the direction of the beam can be remotely controlled withoutaltering the frequency.

The frequency band of the antenna or, in other words, the frequencyrange over which the gain of the antenna is at its maximum can beincreased by increasing the dimensions of links 3 and connection parts 6continuously, so that the dimensions at one end of the antenna aresmallest and they increase by approximately 2 percent in each link andin each intermediate element when moving towards the other end. Such astructure is shown in FIG. 5.

The range of operating frequencies can also be increased by using thedesign shown in FIG. 6. In every second link 3 and intermediate element6 the lengths of the parts are 10 percent larger than in theadjacentlinks.

The width of the beam of the antenna, in the plane of the longitudinalantenna axis, can be adjusted by altering the total length of theantenna. A longer antenna gives a narrower beam than a short one. Thewidth of the radiation beam in the direction perpendicular to thelongitudinal axis can be narrowed conventionally, by'connecting antennasin parallel to give an antenna array. The feed points of the variousantenna elements are connected to each other using conventional parallelconnecting methods for loads, for example with cables of equal length.Parallel antenna elements can also be located quite close to each otherand interconnected electrically as shown in FIG. 7. In this figure, theelements are connected by means of cables 8 of equal length toconnection point 9, to which point generator 10 or the receiver is alsoconnected. The parallel links 3 are connected to each other at points 11in such a way that the distances between the parallel parts 5 are suchthat the characteristic impedance of the transmission line 12 made up ofthe parallel parts 5 and the ground plane 2 is half the characteristicimpedance of the transmission line made up of parts 4 and the groundplane. The connections and the impedance requirements can also beachieved by the method shown in FIG. 8, in which the connections aremade using parts 12 which have the same physical shape and dimensions asthe connection parts 6 between the adjacent links.

The antennas shown in FIGS. 1 and 3 operate with linear polarization.Using two antennas in accordance with FIG. 3, in which the links 3 areparallelograms, elliptical polarization can be achieved, and two typesof circular polarization as limit cases, as shown in FIG. 9. With twochain antennas in which the links 3 are parallelograms of similar shapebut are inclined in opposing directions, the feeding points 7 areconnected to "connection point 9 by means of connection transmissionlines 8 so that there is an additional phase shift element 13 in one ofthem. Measurements have shown that the radiation pattern of the antennaarray shown in FIG. 9 is in the plane through the mirror image axis 14of the antenna and, in general, is elliptically polarized. In the casewhere the acute angle a of the parallelograms is 45 and the additionalphase shift is 13 90, the radiation is circularly polarized. For othervalues of a and additional phase shift, the radiation is elliptically orlinearly polarized. Both of the oblique chains shown in FIG. 9 can alsobe replaced by antenna arrays formed, by means of parallel connections,of corresponding chain antennas.

When pure circular polarization is required, the direction of theradiation beam must also be taken into account. In general, the acuteangle a of the parallelograms can be computed from the formula cot a sin0, where 9 is the angle of elevation of the main radiation beam. For theantenna shown in FIG'. 9, for example, the radiating elements 5 and 6have a length of 0.4 wavelengths, parts 4 have a length of onewavelength, the angle of elevation 0 isapproximately 70 and the angle ofinclination a is approximately 47 According to FIG. 7, the parts 5 areinterconnected at the end points 11 thereof whereas, according to FIG.8, said parts 5 are interconnected along their entire length 12.

What I claim is:

l. A travelling wave chain antenna having a radiation beam, thedirection of hwich can be varied by altering frequency, comprising:

a. a ground plane;

b. a plurality of four-sided links made of conducting material and beinglocated in sequence to forma part ofa chain structure, said linksincluding longer and shorter sides;

c. a cable for feeding the antenna from one end, and including a firstconductor connected to one end of the chain structure and a secondconductor connected to the ground plane; and

d. connection parts arranged between the links and electricallyconnecting the center points of the longer side of each adjacent link,said connection parts being parallel to the shorter sides of the linksand arranged in a common plane at least substantially orthogonal to theground plane.

2. A chain antenna in accordance with claim 1 wherein the end of theantenna opposite said one end is open.

3. A chain antenna in accordance with claim 1 comprising a loadimpedance and wherein the end of the antenna opposite said one end isloaded with said load impedance which is connected between the end ofthe antenna and the ground plane.

4. A chain antenna in accordance with claim 1 wherein the links arearranged in a straight row, such that the connection parts are at rightangles to the longer sides of the links.

5. A chain antenna in accordance with claim 1 wherein the links arearranged in an oblique row such that the connection parts are at anangle to the longer sides of the links.

6. A chain antenna in accordance with claim 1 wherein the connectionparts are so constructed that the characteristic impedance of thetransmission line formed by the connection parts and the ground plane isconsiderably smaller than the characteristic impedance of thetransmission line formed by the sides of the links and the ground plane.

7. A chain antenna in accordance with claim 1 wherein, at the middlefrequency of the operating range, the electrical length of the longersides of the links is approximately one wavelength and the electricallength of the shorter sides and the connection parts between the linksis approximately 0.25 to 0.75 wavelengths, and the distance of the chainstructure from the ground plane is constant and approximately 0.1wavelengths.

8. A chain antenna in accordance with claim 1 wherein the characteristicimpedance of the transmission line formed by the connection partsbetween the links and the ground plane is half the characteristicimpedance of the transmission line formed by the sides of the links andthe ground plane.

9. A chain antenna in accordance with claim 1 wherein the radiatingstructure, consisting of the links and connection parts between thelinks and the ground plane are curved in relation to each other.

10. A wide band chain antenna in accordance with claim 1 wherein thelengths of the sides of the foursided links and of the connection partsbetween the links increase sequentially so that each change in length isapproximately 2 percent.

11. A wide band chain antenna in accordance with claim 1 whereintheshorter sides of the links in the antenna chain and the connection partsbetween the links are of length I +1, in every alternate link or linkconnection, and of length I I in the other alternate links or linkconnections, and wherein, at the middle frequency of the operatingrange, the longer parts of the links have a length of approximately 1wavelength, 1 having a length of approximately half a wavelength and 1generally having a length of between 0.05 and 0.40 wavelengths, thelarger value of 1 giving an antenna of wide bandwidth and the smallervalue giving an antenna of narrower bandwidth.

12. A chain antenna in accordance with claim 1 wherein the links areparallelograms.

13. A chain antenna in accordance with claim 1 wherein the distance ofthe ground plane from the radiating structure increases in such a mannerthat the distance is at its smallest at said one end and at its greatestat the opposite end of the antenna, so that the distance of the groundplane from the radiating structure can vary from 0.05 wavelengths to0.30 wavelengths depending on the total length of the chain.

14. An antenna array comprising a plurality of chain antennas inaccordance with claim 1 wherein the adjacent antenna chains areelectrically connected to each other at the shorter sides of theadjacent links so that the characteristic impedance of the transmissionline formed by the common sides of the links and the ground plane isapproximately half the characteristic impedance of the transmission lineformed by the longer sides of the links and the ground plane and thatthe said one ends of the parallel chains are connected to the generatorwhen transmitting or to the receiver for reception by means ofconventional parallel coupling methods for loads. 7

15. An antenna array in accordance with claim 14 wherein the connectionparts between the successive and adjacent links are similar.

16. An antenna array consisting of chain antennas in accordance withclaim 12 wherein elliptical polarization, and its limit cases, bothcircular polarization and linear polarization, are achieved using twosaid antennas consisting of links of parallelogram shape, in which theparallelograms are identical and the longer sides of the parallelogramsare parallel to each other, the shorter sides being approximatelyperpendicular to each other and the antennas being mirror images of eachother in relation to an axis which is perpendicular to the longer sidesof theparallelograms, these being parallel to each other, and in whichthe said one ends of the antennas are connected to the connection pointby means of transmission lines, one of which includes a phase shiftelement which causes a fixed or adjustable phase shift between the partsin the antenna array having different directions.

17. An antenna array consisting of chain antennas in accordance withclaim 13 wherein elliptical polarization, and its limit cases, bothcircular polarizations and linear polarization, are achieved using twosaid antennas consisting of links of parallelogram shape, in which theparallelograms are identical and the longer sides of the parallelogramsare parallel to each other, the shorter sides being approximatelyperpendicular to each other and the antennas being mirror images of eachother in relation to an axis which is perpendicular to the longer sidesof the parallelograms, these being parallel to each other, and in whichthe said one ends of the antennas are connected to the connection pointby means of transmission lines, one of which includes aphase shiftelement which causes a fixed or adjustable phase shift between the partsin the antenna array having different directions.

1. A travelling wave chain antenna having a radiation beam, thedirection of hwich can be varied by altering frequency, comprising: a. aground plane; b. a plurality of four-sided links made of conductingmaterial and being located in sequence to form a part of a chainstructure, said links including longer and shorter sides; c. a cable forfeeding the antenna from one end, and including a first conductorconnected to one end of the chain structure and a second conductorconnected to the ground plane; and d. connection parts arranged betweenthe links and electrically connecting the center points of the longerside of each adjacent link, said connection parts being parallel to theshorter sides of the links and arranged in a common plane at leastsubstantially orthogonal to the ground plane.
 2. A chain antenna inaccordance with claim 1 wherein the end of the antenna opposite said oneend is open.
 3. A chain antenna in accordance with claim 1 comprising aload impedance and wherein the end of the antenna opposite said one endis loaded with said load impedance which is connected between the end ofthe antenna and the ground plane.
 4. A chain antenna in accordance withclaim 1 wherein the links are arranged in a straight row, such that theconnection parts are at right angles to the longer sides of the links.5. A chain antenna in accordance with claim 1 wherein the links arearranged in an oblique row such that the connection parts are at anangle to the longer sides of the links.
 6. A chain antenna in accordancewith claim 1 wherein the connection parts are so constructed that thecharacteristic impedance of the transmission line formed by theconnection parts and the ground plane is considerably smaller than thecharacteristic impedance of the transmission line formed by the sIdes ofthe links and the ground plane.
 7. A chain antenna in accordance withclaim 1 wherein, at the middle frequency of the operating range, theelectrical length of the longer sides of the links is approximately onewavelength and the electrical length of the shorter sides and theconnection parts between the links is approximately 0.25 to 0.75wavelengths, and the distance of the chain structure from the groundplane is constant and approximately 0.1 wavelengths.
 8. A chain antennain accordance with claim 1 wherein the characteristic impedance of thetransmission line formed by the connection parts between the links andthe ground plane is half the characteristic impedance of thetransmission line formed by the sides of the links and the ground plane.9. A chain antenna in accordance with claim 1 wherein the radiatingstructure, consisting of the links and connection parts between thelinks and the ground plane are curved in relation to each other.
 10. Awide band chain antenna in accordance with claim 1 wherein the lengthsof the sides of the four-sided links and of the connection parts betweenthe links increase sequentially so that each change in length isapproximately 2 percent.
 11. A wide band chain antenna in accordancewith claim 1 wherein the shorter sides of the links in the antenna chainand the connection parts between the links are of length l + l1 in everyalternate link or link connection, and of length l - l1 in the otheralternate links or link connections, and wherein, at the middlefrequency of the operating range, the longer parts of the links have alength of approximately 1 wavelength, l having a length of approximatelyhalf a wavelength and l1 generally having a length of between 0.05 and0.40 wavelengths, the larger value of l1 giving an antenna of widebandwidth and the smaller value giving an antenna of narrower bandwidth.12. A chain antenna in accordance with claim 1 wherein the links areparallelograms.
 13. A chain antenna in accordance with claim 1 whereinthe distance of the ground plane from the radiating structure increasesin such a manner that the distance is at its smallest at said one endand at its greatest at the opposite end of the antenna, so that thedistance of the ground plane from the radiating structure can vary from0.05 wavelengths to 0.30 wavelengths depending on the total length ofthe chain.
 14. An antenna array comprising a plurality of chain antennasin accordance with claim 1 wherein the adjacent antenna chains areelectrically connected to each other at the shorter sides of theadjacent links so that the characteristic impedance of the transmissionline formed by the common sides of the links and the ground plane isapproximately half the characteristic impedance of the transmission lineformed by the longer sides of the links and the ground plane and thatthe said one ends of the parallel chains are connected to the generatorwhen transmitting or to the receiver for reception by means ofconventional parallel coupling methods for loads.
 15. An antenna arrayin accordance with claim 14 wherein the connection parts between thesuccessive and adjacent links are similar.
 16. An antenna arrayconsisting of chain antennas in accordance with claim 12 whereinelliptical polarization, and its limit cases, both circular polarizationand linear polarization, are achieved using two said antennas consistingof links of parallelogram shape, in which the parallelograms areidentical and the longer sides of the parallelograms are parallel toeach other, the shorter sides being approximately perpendicular to eachother and the antennas being mirror images of each other in relation toan axis which is perpendicular to the longer sides of theparallelograms, these being parallel to each other, and in which thesaid one ends of the antennas are connected to the connection point bymeans of tRansmission lines, one of which includes a phase shift elementwhich causes a fixed or adjustable phase shift between the parts in theantenna array having different directions.
 17. An antenna arrayconsisting of chain antennas in accordance with claim 13 whereinelliptical polarization, and its limit cases, both circularpolarizations and linear polarization, are achieved using two saidantennas consisting of links of parallelogram shape, in which theparallelograms are identical and the longer sides of the parallelogramsare parallel to each other, the shorter sides being approximatelyperpendicular to each other and the antennas being mirror images of eachother in relation to an axis which is perpendicular to the longer sidesof the parallelograms, these being parallel to each other, and in whichthe said one ends of the antennas are connected to the connection pointby means of transmission lines, one of which includes a phase shiftelement which causes a fixed or adjustable phase shift between the partsin the antenna array having different directions.